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Abstract:

Techniques for reducing the number of shots required by a radiation beam
writing tool to write a pattern, such as fractured layout design, onto a
substrate. One or more apertures are employed by a radiation beam writing
tool to write a desired pattern onto a substrate using L-shaped images,
T-shaped images, or some combination of both. By reducing the number of
shots required to write a pattern onto a substrate, various
implementations of the invention may reduce the write time and/or write
complexity of the write process.

Claims:

1. A method of writing patterns onto a substrate, comprising projecting a
beam of radiation through at least aperture onto a substrate; and
arranging the beam of radiation relative to the at least one aperture to
form a plurality of images on the substrate, such that at least a portion
of the images have compound-trapezoidal concave shapes; and the plurality
of images forms a pattern made up of convex trapezoidal shapes.

6. The method recited in claim 1, wherein the substrate is a blank
photolithographic mask.

7. The method recited in claim 1, wherein the substrate is a
semiconductor device substrate.

8. The method recited in claim 1, wherein is a microelectromechanical
system substrate.

9. The method recited in claim 1, further comprising arranging the beam
of radiation relative to the at least one aperture by directing a first
portion of the beam of radiation through a first aperture to control
sizes of the images, and directing a second portion of the beam of
radiation through a second aperture to control shapes of the images.

[0002] The present invention is directed to the use of radiation beams to
write patterns onto a substrate, such as a photolithographic mask blank
or a semiconductor device wafer. Various implementations of the invention
may be particularly useful for reducing the amount of time required to
write a desired pattern onto a substrate.

BACKGROUND OF THE INVENTION

[0003] Microdevices, such as integrated electronic circuits and
microelectromechanical system (MEMS) are used in a variety of products,
from automobiles to microwaves to personal computers. Designing and
fabricating microdevices typically involves many steps, known as a
"design flow." The particular steps of a design flow often are dependent
upon the type of microcircuit being designed, its complexity, the design
team, and the microcircuit fabricator or foundry that will manufacture
the microcircuit. For example, if the microdevice is a complex integrated
circuit, then various software and hardware "tools" typically will be
used to verify the device's design prior to manufacture, to confirm that
the manufactured circuit will operate as intended.

[0004] During the microdevice design flow process, a physical design for
the device will be created describing the specific geometric elements
that will make up the device. This type of design often is referred to as
a "layout" design. For example, if the microdevice is an integrated
circuit, then the geometric elements will define the shapes that will be
created in various materials to actually manufacture the circuit device
components (e.g., contacts, gates, interconnect lines, etc.) making up
the circuit. While the geometric elements may have any desired shapes,
such as circular and elliptical shapes, they typically will be polygons.
Layout tools (often referred to as "place and route" tools), such as
Mentor Graphics' IC Station or Cadence's Virtuoso, are commonly used for
both of these tasks.

[0005] After the layout design has been finalized, it is converted into a
format that can be employed to manufacture the microdevice. For example,
the microdevice may be manufactured using a photolithographic
manufacturing process. With this manufacturing process, the layout design
data will be converted into a format that can be used by a mask writing
tool to create a mask for use in a photolithographic manufacturing
process. Masks are typically made using tools that expose a blank mask
substrate to a beam of radiation, such as an electron or laser beam, to
create opaque, translucent or transparent patterns. Alternately, the
microdevice may be manufactured by using a beam of radiation to directly
write patterns onto a device substrate, by, for example, energizing
portions of a resist material formed over the substrate's surface prior
to an etching process. With this type of direct-write manufacturing
process, the layout design data similarly will be converted into a format
that can be used by a radiation beam tool to write the desired patterns
onto a substrate.

[0006] Most radiation beam writing tools are able to only write certain
kinds of polygons, however, such as right triangles, rectangles or other
trapezoids. Moreover, the sizes of the polygons are limited physically by
the maximum beam aperture size available to the radiation beam writing
tool. Accordingly, larger geometric elements in a layout design, or
geometric elements that are not basic right triangles, rectangles or
trapezoids (which typically is a majority of the geometric elements in a
layout design) are "fractured" into smaller, more basic "atomic" polygons
that can be written by radiation beam writing tool. Typically, these
atomic polygons will be rectangles. Once the layout design has been
fractured into atomic shapes, the layout design data can be converted to
a format compatible with a particular radiation beam writing tool.
Examples of such formats are MEBES, for raster scanning machines
manufactured by ETEC, an Applied Materials Company, the ".MIC" format
from Micronics AB in Sweden, and various vector scan formats for Nuflare,
JEOL, and Hitachi machines, such as VSB12 or VSB12.

[0007] With conventional radiation beam writing tools, each atomic shape
may be formed with a single beam exposure through one or more apertures
that are configured for the desired atomic shape. This exposure is often
referred to as a "shot." The operating time of radiation beam writing
tool typically will be proportional to the number of shots required to
write the desired pattern. Accordingly, as microdevice designs become
more complex, the amount of time required to create a photolithographic
mask or manufacture a microdevice using a direct-writing technique has
increased. Further, with photolithographic manufacturing, some resolution
enhancement techniques used to improve the manufacturing process, such as
optical process correction (OPC), have dramatically increased the number
of atomic shapes in fractured layout designs. As a result, creating a set
of photolithographic masks required to manufacture an integrated circuit
microdevice may cost millions of dollars.

BRIEF SUMMARY OF THE INVENTION

[0008] Aspects of the invention relate to techniques for reducing the
number of shots required by a radiation beam writing tool to write a
pattern, such as fractured layout design, onto a substrate. According to
various implementations of the invention, one or more apertures are
employed by a radiation beam writing tool to write a desired pattern onto
a substrate using L-shaped images, T-shaped images, or some combination
of both. For example, some implementations of the invention may analyze
the atomic shapes in a pattern to identify adjacent rectangular atomic
shapes that can be combined into an L-shape or a T-shape. The radiation
beam writing tool can then write these atomic shapes onto a substrate in
a single shot by forming an image on the substrate corresponding to the
L-shape or T-shape. By reducing the number of shots required to write a
pattern onto a substrate, various implementations of the invention may
reduce the write time and/or write complexity of the write process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 illustrates an example of a pattern segment that has been
divided into rectangular atomic shapes.

[0010]FIG. 2 illustrates the pattern segment shown in FIG. 1 using a
combination of L-shapes and rectangular shapes according to various
examples of the invention.

[0016] FIG. 8 illustrates another example of apertures that may be
employed in the radiation beam writing tool shown in FIG. 6 according to
various examples of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Overview

[0017]FIG. 1 illustrates an example of a pattern segment 101 that has
been divided into rectangular atomic shapes 103A-103E. As will be
appreciated by those of ordinary skill in the art, the pattern segment
101 is representative of many pattern segments that may be found in a
physical microdevice design, such as a layout design for an integrated
circuit. As previously noted, each of the atomic shapes 103A-103E are
rectangular, as is typical for conventional radiation beam writing tools.
As will be explained in more detail below, various examples of the
invention represent patterns to be written onto a substrate using one or
more L-shapes, one or more T-shapes, or some combination thereof. For
example, FIG. 2 illustrates the pattern 101 according to various examples
of the invention by using a combination of L-shapes and rectangular
shapes. More particularly, as seen in this figure, the rectangular atomic
shape 103A and the rectangular atomic shape 103B have been combined into
a single L-shape 201, while the rectangular atomic shape 103D and the
rectangular atomic shape 103E have been combined into a single L-shape
203.

[0018] As will also be discussed in more detail below, various
implementations of the invention provide radiation beam writing tools
that can easily project an L-shaped image or a T-shaped image onto a
substrate. Thus, by employing a radiation beam writing tool configured to
write L-shaped images onto a substrate, the pattern segment 101 can be
written according to various implementations of the invention using only
three shots corresponding to the shapes 102C, 201 and 203 shown in FIG. 1
(i.e., a shot reduction of 40%). FIG. 3 illustrates a larger pattern
segment 301, which also is representative of many pattern segments that
may be found in a physical microdevice design. As seen in this figure,
this larger pattern segment 301 can be divided into a plurality of
rectangular shapes 303 and L-shapes 305 that can be written by a
radiation beam writing tool according to various examples of the
invention.

Radiation Beam Writing Tool

[0019]FIG. 4 illustrates an example of a conventional radiation beam
writing tool 401. Typically, the radiation beam writing tool 401 will
include a radiation source (not shown) that produces a beam 403 of
radiation. The radiation beam 403 may be a beam of electrons (e.g., for
an e-beam writer). The radiation beam 403 also may be a beam of
electromagnetic radiation, such as visible light or ultraviolet light
(e.g., a laser writer). The radiation beam 403 may be collimated, it may
be focused using conventional lensing techniques, or it may employ some
combination thereof.

[0020] The radiation beam 403 is partially blocked by an aperture platform
405 defining an aperture 407 therethrough. The aperture 407 allows
through only a first beam portion 409 of the radiation beam 403. If the
radiation beam 403 is an electronic beam, then the direction of the first
beam portion 409 is then controlled by a set of electronic deflectors
411. More particularly, the deflectors 411 direct the first beam portion
409 so that some or all of it passes through a second aperture 415 in a
second aperture platform 413.

[0021] Thus, the first beam portion 409 forms an image 417 on the second
aperture platform 413 that partially or fully overlaps the second
aperture 415, thereby segmenting a second beam portion 419 that passes
through the second aperture 415. This second beam portion 419 forms an
image 421 or shot on a substrate (not shown). By directing the first beam
portion 409 from the first aperture 407 to the second aperture 415, the
deflectors 411 can control the specific shape and size of the image 421
written onto a substrate. Of course, it should be appreciated that other
types of radiation beam writing tools may employ different
configurations. For example, some radiation beam writing tools might move
the first aperture 407 and the second aperture 415 relative to each
other, rather than (or in addition to) controlling the direction of the
first beam portion 409. Further, those of ordinary skill in the art will
appreciate that, if the radiation beam 403 is an electromagnetic
radiation beam such as a laser, then the radiation beam writing tool 401
may use a different arrangement to pass the radiation beam 403 through
one or more apertures to form the image 421.

[0022] As will be appreciated by those of ordinary skill in the art, the
apertures 407 and 415 conventionally have opposing parallel edges, which
constrain the image 421 to an isothetic trapezoidal shape. Moreover, in a
typical microdevice design, shape edges within the design usually are
parallel to an x-axis or y-axis of the image coordinate system employed
to create the design, thereby requiring the radiation beam writing tool
401 to form rectangular-shaped images 421 in order to write the design.
As a result, most conventional radiation beam writing tools relay upon
this arrangement to enhance performance.

Radiation Beam Writing Tool for Writing L-Shaped or T-Shaped Images

[0023]FIG. 5 illustrates an example of a radiation beam writing tool 501
that may be employed to write L-shaped images and T-shaped images
according to various examples of the invention. The radiation beam
writing tool 501 may generally include the major components of the
radiation beam writing tool 401, such as a radiation source (not shown)
that produces a beam 403 of radiation. The radiation beam 403 may be a
beam of electrons (e.g., for an e-beam writer). The radiation beam 403
also may be a beam of electromagnetic radiation, such as visible light or
ultraviolet light (e.g., a laser writer). The radiation beam 403 may be
collimated, it may be focused using conventional lensing techniques, or
it may employ some combination thereof. As seen in FIG. 5, the radiation
beam writing tool 501 also will include the first aperture platform 405
defining the first aperture 407, the deflectors 411, and the second
aperture platform 413 defining the second aperture 415.

[0024] In addition, the radiation beam writing tool 501 further includes a
second set of electronic deflectors 503 and a third aperture platform 505
defining a third aperture 507 therethrough. As show in FIG. 5, the
aperture platform 505 includes four aperture tabs 509A-509C sized and
positioned to provide the aperture 507 with a symmetric T-shape. As used
herein, the terms "T-shape," "t-shape" and other variations will broadly
refer to a generic category of shapes having one substantially straight
portion orthogonally intersect or pass through another substantially
straight portion. Thus the terms "T-shape," "t-shape" and other
variations will encompass all of the following general shapes: , , , and
.

[0025] In operation the electronic deflectors 503 will direct the second
beam portion 419 so that some or all of it passes through the third
aperture 507 in the third aperture platform 505. Thus, the second beam
portion 409 forms the image 421 on the aperture platform 505 so that the
image 421 partially or fully overlaps the aperture 507, thereby
segmenting a third beam portion 511 that passes through the third
aperture 507. This third beam portion 511 forms an image 513 on a
substrate (not shown).

[0026] As previously noted, the aperture 507 has a t-shape. By directing
the second beam portion 409 through the t-shaped aperture 507, the
deflectors 503 can control the specific shape and size of the image 421
written onto a substrate. More particularly, if the deflectors 503 direct
the second beam portion 409 onto the aperture 507 so that some of the
second beam portion 409 is blocked by a single aperture tab 509, then the
image 513 created by the third beam portion 511 will have an L-shape. For
example, in FIG. 5, some of the second beam portion 409 is blocked by the
aperture tab 509A, causing the image 513 to have an L-shape with the
concave region facing up and to the right in the illustration. Moreover,
by controlling which areas of the image 513 are blocked by the aperture
tab 509, the radiation beam writing tool 501 can adjust the width and
length of each of the portions in the L-shape.

[0027] Similarly, if the deflectors 503 direct the second beam portion 409
onto the aperture 507 so that some of the second beam portion 409 is
blocked by a two or four aperture tabs 509, then the image 513 created by
the third beam portion 511 will have an T-shape. If some of the second
beam portion 409 is blocked by only two aperture tabs 509, then the image
will have a , , and shape. If some of the second beam portion 409 is
blocked by all four aperture tabs 509, then the image will have a shape.
Again, by controlling which areas of the image 513 are blocked by the
aperture tab 509, the radiation beam writing tool 501 can adjust the
width and length of each of the portions in the t-shape. Of course, by
directing the second beam portion 409 onto the aperture 507 so that none
of the second beam portion 409 is blocked by an aperture tab 509, then
the image 513 created by the third beam portion 511 will have an
rectangular shape (i.e, either a rectangle or a square, depending upon
the area of the first beam portion blocked by the second aperture 415.

[0028] In this manner, the radiation beam writing tool 501 can form a
variety of t-shaped images, L-shaped images, and rectangular images to
use as shots in writing a pattern onto a substrate. Of course, further
implementations of the radiation beam writing tool 501 may employ
additional features to enhance the range of producible shapes. For
example, some implementations of the radiation beam writing tool 501 may
provide adjustable aperture tabs 509 that can be lengthened, broadened,
or both, so as to provide greater variety in the range of possible
lengths and widths of the legs in L-shaped and t-shaped images.

[0029]FIG. 6 illustrates another example of a radiation beam writing tool
601 that may be employed to write L-shaped images and T-shaped images
according to various examples of the invention. Like the radiation beam
writing tool 501, the radiation beam writing tool 601 may generally
include the major components of the radiation beam writing tool 401, such
as a radiation source (not shown) that produces a beam 403 of radiation.
The radiation beam 403 may be a beam of electrons (e.g., for an e-beam
writer). The radiation beam 403 also may be a beam of electromagnetic
radiation, such as visible light or ultraviolet light (e.g., a laser
writer). The radiation beam 403 may be collimated, it may be focused
using conventional lensing techniques, or it may employ some combination
thereof. As seen in FIG. 6, however, the second aperture platform 413
defines a plurality of apertures 415 with different shapes. For example,
in the illustrated implementation, the second aperture platform defines a
rectangular aperture 415A and an irregularly shaped aperture 415B. As
shown in more detail in FIG. 7, the irregularly shaped aperture 415B has
a plurality of orthogonal legs of different widths and lengths.
Accordingly, by controlling the first beam portion 409 so that the image
417 overlaps different regions of the irregularly shaped aperture 415B,
the radiation beam writing tool 601 can vary the shape of the second beam
portion 419 and the resulting image 421 that is written onto the
substrate (not shown). By providing multiple apertures 415 with a variety
of different irregular shapes, the radiation beam writing tool 601 will
allow a user to create an even wider variety of shapes for the image 421.

[0030] FIG. 8 illustrates yet another example of a second aperture
platform 413 that may be employed with the radiation beam writing tool
601. As seen in this figure, the second aperture platform 413 includes an
aperture 415C with four aperture tabs 801A-801C. As with the aperture 509
illustrated in FIG. 5 discussed above, the aperture tabs 801 provide the
aperture 415C with a symmetric t-shape. As also previously discussed with
respect to the implantation shown in FIG. 5, the deflectors 411 can be
used to determine how much of the image 417 overlaps with one or more of
the aperture tabs 801, thereby controlling whether the second beam
portion 419 and the resultant image 421 have an L-shape, a -shape, a
shape, a -shape, or a -shape. Further, various implementations of the
radiation beam writing tool 601 may provide a plurality of apertures
415C, each with a different width and/or length for one or more of the
aperture tabs 801. For example, some implementations of the invention may
provide a multiple series of apertures 415C where the length of each
aperture tab 801 increases by, e.g., 1 nanometer from each series to each
series. Each series may then contain multiple apertures 415C where the
width of each aperture tab 801 increases by, e.g., 1 nanometer from an
aperture 415C to the next aperture 415C in the series. In this way, the
plurality of apertures 415C will allow the radiation beam writing tool
601 to write the image 421 in a wide variety of L-shapes and t-shapes.

Pattern Generation

[0031] As discussed in detail above, various implementations of the
invention allow a radiation beam writing tool to write a pattern onto a
substrate using a combination of rectangularly-shaped shots, L-shaped
shots, and t-shaped shots. The generation of a pattern made up of
rectangular shapes and L-shapes that may be employed according to various
examples of the invention will now be discussed with regard to the method
shown in the flowchart shown in FIG. 9.

[0032] Initially, in operation 901, microdevice design data is fractured
into conventional atomic shapes. With various implementations of the
invention, this fracturing process may be performed by a fracturing
module in a pattern generation tool according to various implementations
of the invention. Alternately, some or all of the microdevice design data
can be fractured into conventional atomic shapes by a separate fracturing
tool, and provided to a pattern generation tool according to various
implementations of the invention from an outside source. As will be
appreciated by those of ordinary skill in the art, conventional
microdevice design data fracturing processes are well known in the art,
and will not be discussed in further detail.

[0033] Next, in operation 903, non-rectangular trapezoids are filtered
from the fractured microdevice design data. Again, this operation may be
performed by a filtering module in a pattern generation tool according to
various implementations of the invention. Alternately, some or all of the
non-rectangular shapes may be filtered from the fractured microdevice
design data by a separate filtering tool, and some or all of the
filtered, fractured microdevice design data may be provided to a pattern
generation tool according to various implementations of the invention
from an outside source.

[0034] In operation 905, a scanline module in a pattern generation tool
according to various implementations of the invention uses a scanline
process to identify adjacent pairs of rectangular atomic shapes in the
fractured pattern. Then, in operation 907, a pair identification module
in a pattern generation tool according to various implementations of the
invention identifies adjacent pairs of rectangular shapes are checked to
determine if they comply with specified permissibility rules.

[0035] As will be appreciated by those of ordinary skill in the art, in
the "fracturing" operation for variable-shaped beam mask writing, the
creation of narrow trapezoids with one or more long sides coincident with
the target shape edge are avoided. With various implementations of the
invention, the same criterion is applied in creating L-shaped images in
the pattern to be written to a substrate. The underlying physical effect
implies an additional requirement, however, as exposed energy is less in
features narrower than some characteristic width. In a conventional
fracturing process, this can be addressed by the rule mentioned above or
by dose or exposure time adjustment. With an L-shaped shot having one
narrow leg and one wide leg, however, the disparity cannot be easily
corrected. One leg will suffer reduced or too much written energy
density.

[0036] To ensure uniform intensity of exposure of an entire L-shot, a
pattern generation tool according to various implementations of the
invention may employ a constraint to control the width of the legs of an
L-shaped shot. Specifically, with some implementations, given a parameter
`s`, neither leg may be both narrower than and longer than s. The value
of s is usually the "small value" parameter used to characterize narrow
trapezoids in conventional fracture. Further, the entire L-shot is
constrained to fit within a square whose side length is the maximum shot
size for the mask writer.

[0037] These constraints on the designation of L-shots are similar to
those used with cell-projection apertures. Both exhibit concave corners
and substantial complexity confined to a local spatial extent.
Accordingly, those of ordinary skill in the art will appreciate that any
compensation or correction techniques used for cell projection may also
apply to various implementations of the invention.

[0038] Forming an L-shot should take no longer than the formation of a
rectangular or trapezoidal shot, since the times to control the two
deflectors overlap. An additional high-speed data channel is required in
order to drive the new deflector. Each L-shot imparts the exposure of two
rectangular shots, however; i.e., each L-shot eliminates a conventional
fracture shot. In addition, if one of the rectangular shots was narrow,
then extra exposure time or dose may also be obviated. Thus, various
implementations of the invention provide the ability to print small
corner notches that would normally be considered a less than ideal
feature.

[0039] Conventional trapezoidal exposure in a shaped-beam writer has a
well understood model of the error for each shot. The shaping deflector
between the two shaping apertures will suffer some errors `e` in each
dimension (assumed isotropic for simplicity), respectively, which make
the width and height of the shot random variables. The placement
deflectors and stage positioning error then create placement errors `p1`
in each dimension.

[0040] The error model for L-shot exposure is more complicated, as
illustrated in FIG. 10. Two deflectors are used in shaping, resulting in
shaping errors `e1` and `e2`. Placement error is unchanged, since the
relevant apparatus is unchanged. In the figure one sees that some errors
are compounded while others are reduced. For instance, the dimensions
between a `notch` edge and the opposite edge are now sums of two
independent random variables. But the dimensions between "end" edges and
their opposites are now single random variables, as opposed to being sums
of two random variables in the conventional case, and the shared "end"
edge is now formed by a single aperture in one exposure. In any case, the
major component of shot edge error--the placement error--is unchanged
between the new method and trapezoidal exposure.

[0041] Lastly, in operation 909, pairs of adjacent rectangles that comply
with the relevant permissibility rules are combined in the pattern. In
this manner, a conventional fractured pattern can be converted to atomic
shot shapes that can be employed by a beam writing tool according to
various implementations of the invention. Further, while implementations
of pattern generating tools were described above with respect to L-shaped
shots, it should be appreciated that the relevant techniques and criteria
could likewise be employed according to various embodiments of the
invention to generate patterns with additional or alternate t-shaped
shots.

Exemplary Operating Environment

[0042] The execution of various pattern generating processes according to
embodiments of the invention described may be implemented using
computer-executable software instructions executed by one or more
programmable computing devices, by one or more computers executing
software instructions, by software instructions for programming one or
more computers stored on a non-transitory computer-readable medium, or
some combination thereof. Various examples of the invention may be
implemented through the execution of software instructions by a computing
device, such as a programmable computer. Accordingly, FIG. 11 shows an
illustrative example of a computing device 1101. As seen in this figure,
the computing device 1101 includes a computing unit 1103 with a
processing unit 1105 and a system memory 1107. The processing unit 1105
may be any type of programmable electronic device for executing software
instructions, but will conventionally be a microprocessor. The system
memory 1107 may include both a read-only memory (ROM) 1109 and a random
access memory (RAM) 1111. As will be appreciated by those of ordinary
skill in the art, both the read-only memory (ROM) 1109 and the random
access memory (RAM) 1111 may store software instructions for execution by
the processing unit 1105.

[0043] The processing unit 1105 and the system memory 1107 are connected,
either directly or indirectly, through a bus 1113 or alternate
communication structure, to one or more peripheral devices. For example,
the processing unit 1105 or the system memory 1107 may be directly or
indirectly connected to one or more additional memory storage devices,
such as a "hard" magnetic disk drive 1115, a removable magnetic disk
drive 1117, an optical disk drive 1119, or a flash memory card 1121. The
processing unit 1105 and the system memory 1107 also may be directly or
indirectly connected to one or more input devices 1123 and one or more
output devices 1125. The input devices 1123 may include, for example, a
keyboard, a pointing device (such as a mouse, touchpad, stylus,
trackball, or joystick), a scanner, a camera, and a microphone. The
output devices 1125 may include, for example, a monitor display, a
printer and speakers. With various examples of the computer 1101, one or
more of the peripheral devices 1115-125 may be internally housed with the
computing unit 1103. Alternately, one or more of the peripheral devices
1115-125 may be external to the housing for the computing unit 1103 and
connected to the bus 1113 through, for example, a Universal Serial Bus
(USB) connection.

[0044] With some implementations, the computing unit 1103 may be directly
or indirectly connected to one or more network interfaces 1127 for
communicating with other devices making up a network. The network
interface 1127 translates data and control signals from the computing
unit 1103 into network messages according to one or more communication
protocols, such as the transmission control protocol (TCP) and the
Internet protocol (IP). Also, the interface 1127 may employ any suitable
connection agent (or combination of agents) for connecting to a network,
including, for example, a wireless transceiver, a modem, or an Ethernet
connection. Such network interfaces and protocols are well known in the
art, and thus will not be discussed here in more detail.

[0045] It should be appreciated that the computer 1101 is illustrated as
an example only, and it not intended to be limiting. Various embodiments
of the invention may be implemented using one or more computing devices
that include the components of the computer 1101 illustrated in FIG. 11,
which include only a subset of the components illustrated in FIG. 11, or
which include an alternate combination of components, including
components that are not shown in FIG. 11. For example, various
embodiments of the invention may be implemented using a multi-processor
computer, a plurality of single and/or multiprocessor computers arranged
into a network, or some combination of both.

CONCLUSION

[0046] While the invention has been described with respect to specific
examples including presently preferred modes of carrying out the
invention, those skilled in the art will appreciate that there are
numerous variations and permutations of the above described systems and
techniques that fall within the spirit and scope of the invention as set
forth in the appended claims. For example, while specific terminology has
been employed above to refer to electronic design automation processes,
it should be appreciated that various examples of the invention may be
implemented using any desired combination of electronic design automation
processes.